Hey Ron
I got my spacer from
www.adaptitusa.com (317-856-1810), I gave them a call and they were very helpful. they will make whatever you want/need
a spacer that is 5 X 120 to 5 X 120 (1.75in thick) with 14 X 1.50 studs is needed to clear 4 piston (stock SS) brembo calipers without the "roller skate" pads (earlier model years)
you will need to make it 2.5in thick so the spare will clear the later model roller skate brake pads. it also clears the CTS-V brakes on my car
part # for the GM donut wheel (18x4) I used was #92230888, I think this is the 2013 wheel but I am not positive
the wheels on our Camaros are hub centric. I don't recall the ID of the adapter, but the one I got from adaptit fits fine. it is not real tight on the hub, but I won't be running on it long and for sure will not be putting stress loads on it from cornering. I would be comfortable if the adapter was stud centric.
here's a picture of how close my spare (with the 2.5in spacer) is to the roller skates before I upgraded to the 6 piston calipers